The major objective of this proposed research project is to study in depth the processes of ventilation of the middle ears and sinuses. The purpose is to apply this knowledge as an aid in clinical diagnosis of otorhinological problems. Previous studies we have conducted demonstrate that by using a bilateral negative-positive displacement technique good initial concentrations of a radioactive gas, Xenon-133, can be obtained in the middle ears and sinuses. The rates of egress obtained from these studies have been shown to be reliable measures and repeatable. Rate of egress from these cavities is measured by a Nuclear Chicago Pho Gamma 111-HP scintillation camera interfaced to a Digital Equipment Corporation PDP-15 computer. Technical Associates portable clinical counting systems will be evaluated for their value as diagnostic and research instruments in the study of ventilation. Studies of the middle ear indicated that they yield the same rates of egress as the scintillation camera in direct comparisons. Four miniature (6mm diameter) probes are used to provide data from selected regions of interest. We intend to study many normal subjects to improve the accuracy and reliability of the sample statistics we have obtained to date. We particularly wish to investigate what differences may be obtained in longitudinal studies of children, since hearing problems stem from the high incidence of otological diseases in children. Subjects of our experiments will range in age from six years through adults. We also will pursue before and after studies involving changes in ventilation due to surgical procedures on patients so that the efficacy of the surgery can be asssessed. The portable system will be used to differentiate the ventilation rates of the mastoids from the middle ears. Also, direct comparisons will be made between known abnormal conditions and the normal rates of ventilation we are establishing.